3.2 Symbolic mode

In the symbolic mode, permissions and ownerships are both represented as characters:

• u: the user owner.
• g: the group owner.
• o: the others.
• a: all owners (user, group and others).
• r: read permission.
• w: write permission.
• x: execute permission.
• X: traverse directory.
• t: sticky bit.
• s: set user ID or group ID.

A “mode” consists of a list of at least own owner (user, group or others), an action, and an optional permission list.

Examples:

• chmod u+x file
  Adds execute permission to the user ownher.
• chmod o-w file
  Removes write permission from the others.
• chmod og=rx file
  Sets others and group owner to read and execute permissions.
• chmod -R g+X dir
  Recursively adds directory traverse permission without adding execute permissions to normal (non-directory) files.
• chmod u+s file
  Adds set user ID to file. Anyeone who can execute file will do so as the user owner. This is very dangerous, especially if the user owner is root!